How to use the array modifier with imperial units
You can readily use inches by entering the inches value you need into the offset distance box, as "16 inch". It will automatically convert it to be the corresponding meter value. Or you could go ahead and change the unit system that Blender is currently using.

Refer to the Blender Documentation for more info about the Array modifier.
https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/array.html